Method and system for producing silane

ABSTRACT

This invention relates to a continuous process for the preparation of silane by catalytic disproportionation of trichlorosilane in a reactive/distillative reaction zone having a catalyst bed of catalytically active solid.

The present invention relates to a continuous process for thepreparation of silane SiH₄ by catalytic disproportionation oftrichlorosilane SiHCl₃ to form SiH₄ and silicon tetrachloride SiCl₄. Theinvention further relates to an installation for carrying out theprocess.

SiH₄ is a very suitable starting material from which, optionally afterfurther purification, very pure silicon of semiconductor grade can bedeposited by thermal decomposition. There is a strongly increasingdemand for ultrapure silicon and thus for pure silane which isrecognized and utilized more and more as a very suitable source ofultrapure silicon.

From the silane preparation processes described in the literature, thetrichlorosilane disproportionation is economically advantageous. The useof amines, especially tertiary amines and hydrochlorides thereof andquaternary ammonium chlorides, both in liquid form (DE 3 500 318) and insolid form, e.g. bound to solid supports, as catalysts is known toaccelerate the disproportionation of the trichlorosilane in aneconomically advantageous manner. The use of amines bound to solidsupports (U.S. Pat. Nos. 4,701,430, U.S. 5,026,533, DE 3 500 318, DE 3311 650) is therefore preferred because the contamination of thereacting silane/chlorosilane gas/liquid phase with amines can be avoidedin this way.

A disadvantage of the liquid catalysts selected in some other existingprocesses is that they are discharged from the reaction section slowlyover time, because they can never be separated completely from thereaction products. The entrained amounts of catalyst give rise toproblems in downstream process steps or, in a circulation system, alsoin upstream process steps, because they can accumulate at certain pointsin the system where they can catalyze undesired reactions, for example.In addition, it is not possible to achieve a very uniform distributionof a liquid catalyst in the column, rather the catalyst will locallyconcentrate owing to its specific vapor pressure. This problem is in noway solved, but at best alleviated, by the use of two catalysts havingdifferent boiling points as proposed in DE 3 500 318.

Attempts have already been made to conduct the disproportionation,which, according to the prior art, is a multistep process, for example atwo-step process, in one step applying the principle of reactivedistillation. Reactive distillation is characterized by a combination ofreaction and distillative separation in a single apparatus, inparticular a column. The continuous distillative removal of thelowest-boiling component respectively in each element of space ensuresthat an optimum difference between the equilibrium state and the actualcontent of lower-boiling components or lowest-boiling component isalways maintained, resulting in a maximum reaction rate (JP-01 317 114).

DE 2 507 864 discloses another process for the preparation of silanewhich comprises introducing trichlorosilane into a bed of an anionexchange resin which is insoluble in the reaction medium and containstertiary amino or quaternary ammonium groups bonded to a carbon atom,maintaining the resin bed at a temperature sufficient to causetrichlorosilane to be disproportionated to form products which rise inthe bed, and silicon tetrachloride which condenses and flows to thecolumn bottom, and maintaining the top part of the bed at a temperatureabove the boiling point of silane and below the boiling point ofmonochlorosilane, and recovering from the bed silane which is virtuallychlorosilane-free.

This process is distinguished from the other known processes by thefollowing features:

-   -   (1) it can be carried out in a single apparatus, i.e. the        desired, enriched products silane and silicon tetrachloride can        be taken off at different points of the same apparatus, and        therefore requires a comparatively low expenditure in terms of        apparatus and energy;    -   (2) it makes it possible to obtain the products silane (in        concentrations of between 96 to 98% of SiH₄) and silicon        tetrachloride (in concentrations of e.g. between 70 to 80% of        SiCl₄) in comparatively high concentration without the need for        further auxiliary units;    -   (3) owing to the solid insoluble catalyst (hereinafter called        catalytically active solid), the introduction of impurities from        the catalyst into the reaction mixture is minimized, the        separation of the catalyst is significantly easier than in the        case of the liquid soluble catalysts, and the accumulation of        volatile, liquid catalysts in certain column parts is strictly        avoided; and    -   (4) the amount of energy required for the separation of the        silanes or chlorosilanes formed in the individual equilibrium        stages of the disproportionation is minimized by the principle        of reactive rectification.

A grave disadvantage of this process described in DE 2 507 864 is thatthe amount of energy utilized for the separation of the silanes orchlorosilanes has to be completely removed at a very low temperaturelevel matched to the condensation temperatures. In fact, DE 2 507 864requires that the temperature at the top of the column be below thecondensation temperature of monochlorosilane SiH₃Cl and that thetemperature in the trichlorosilane SiHCl₃ feed zone be such thattrichlorosilane can be evaporated. Thus, the energy required forevaporating the various chlorosilanes and the silane in the individualsections of the column is actually removed at a temperature below thecondensation temperature of the monochlorosilane, i.e. from below −50°C. to −120° C. However, heat removal at a low temperature level is knownto be costly and requires additional energy, and indeed the lower thetemperature to be set for the coolant, the higher the amount ofadditional energy required.

It is an object of the invention to provide a continuous process and aninstallation for the preparation of silane by catalyticdisproportionation of trichlorosilane to form silane and silicontetrachloride in which the disproportionation proceeds in areactive/distillative manner over catalytically active solids, silaneand silicon-tetrachloride are recovered in comparatively highconcentration, and the disproportionated products are separated andcondensed with minimal expenditure. The heat is to be removedessentially at a temperature level at which the coolant can be usedwhich has a temperature that can be achieved quite easily, and theapparatus and energy required for refrigeration to remove the heat forcondensing the products is to be reduced.

A continuous process for the preparation of silane SiH₄ by catalyticdisproportionation of trichlorosilane SiHCl₃ to form SiH₄ and silicontetrachloride SiCl₄ in a reactive/distillative reaction zone comprisinga catalyst bed of catalytically active solid, into which SiHCl₃ isintroduced and from which lower-boiling SiH₄-containing product formedin the catalyst bed is taken off and condensed in an overhead condenserand discharged as final product, and in which SiCl₄ is formed ashigher-boiling bottom product, is provided which is characterized inthat the lower-boiling product mixture, which has formed in the catalystbed at a pressure of 1 to 50 bar, is subjected to an intermediatecondensation at a temperature in the range from −25° C. to 50° C., andthe SiH₄-containing product mixture which is not condensed in theintermediate condensation is condensed in the overhead condenser.

Suitable catalytically active solids are known and also described in DE2 507 864. For example, they are solids which contain, on a framework ofdivinylbenzene-crosslinked polystyrene, amino or alkyleneamino groupssuch as dimethylamino, diethylamino, ethylmethylamino, di-n-propylamino,di-i-propylamino, di-2-chloroethylamino, di-2-chloropropylamino groupsand hydrochlorides thereof, or trialkylammonium groups formed therefromby methylation, ethylation, propylation, butylation, hydroxyethylationor benzylation, with chloride counterion. In the case of quaternaryammonium salts or protonated ammonium salts it is of course alsopossible to introduce into the process according to inventioncatalytically active solids containing other anions, e.g. hydroxide,sulfate, hydrogensulfate, bicarbonate etc., in the course of time, theseare, however, inevitably converted into the chloride form under thereaction conditions, which also applies to organic hydroxyl groups.

Other suitable solids are those composed of a polyacrylic acidframework, especially a polyacrylamide framework, to which e.g.trialkylbenzylammonium is attached via an alkyl group.

Another group of catalytically active solids which is suitable for theprocess according to the invention are those which have sulfonate groupsattached to a divinylbenzene-crosslinked polystyrene framework, balancedwith tertiary or quaternary ammonium groups as cations.

Macroporous or mesoporous exchange resins are usually more suitable thangel resins. Other suitable catalytically active solids are those whichcarry organic amino groups of the abovementioned type, e.g. those whichhave a 3-siloxypropyldimethylamino group, attached to a solid inorganicframework such as silica or zeolite (U.S. Pat. No. 4,701,430). Suitablecatalytically active solids are usually employed in the form of beads.

A number of suitable activation and pretreatment methods for thesecatalysts are described in the literature.

In a preferred embodiment of the process according to the invention, theSiH₄-containing product mixture is separated from the higher-boilingchlorosilanes present in the mixture prior to condensation of the finalSiH₄ product so as to increase the SiH₄ concentration. The separation ispreferably conducted at a pressure which his higher than that employedin the intermediate condensation, so that the concentration of the SiH₄can be achieved at a higher temperature level and thus less product isto be condensed at a higher SiH₄ concentration. Chlorosilane obtained inthe separation is conveniently returned to the reactive/distillativereaction zone.

The invention and further embodiments thereof are illustrated below withreference to installations for carrying out the process andcorresponding examples.

Specifically, in the drawing:

FIG. 1 shows an installation for the production of silane comprising areactive/distillative reaction zone, an intermediate condenser,integrated rectifying section and, downstream of the rectifying section,an external overhead condenser for condensing silane;

FIG. 2 shows an installation for the production of silane comprising areactive/distillative reaction zone, an intermediate condenser,integrated rectifying section and, downstream of the rectifying section,an external condenser, a separation column downstream of the latter, andan overhead condenser for condensing silane which is connected to theseparation column.

FIG. 3 shows an embodiment with external reactors.

FIG. 1 shows a flow chart for an installation for the continuousproduction of silane SiH₄ which comprises an essentially verticalreaction column 1 having a reactive/distillative reaction zone 2 for thecatalytic disproportionation of trichlorosilane SiHCl₃. Thedisproportionation in the reaction zone 2 is conducted in a catalyst bed2′ which is made of a randomly packed layer of solid bodies ofcatalytically active solid and through which the disproportionationproducts can flow. Instead of a randomly packed layer, the reaction zonemay also contain catalyst bodies in a structured packing. Catalyticallyactive solids are preferably those described in DE 2 507 864, asmentioned above.

The SiHCl₃ is introduced into the reaction column 1 via an inlet 3 whichopens into the column at an appropriate point. In the reaction zone 2,disproportionation of SiHCl₃ yields a lower-boiling SiH₄-containingproduct mixture which ascends in the reaction zone and a higher-boilingSiH₄-containing condensate which descends in the reaction zone.

In the reaction column 1, the higher-boiling SiCl₄-containing condensateexiting from the reaction zone is introduced into a distillativestripping section 4 which is arranged below the reactive/distillativereaction zone 2. From a bottom evaporator 5, arranged below thestripping section, silicon tetrachloride SiCl₄ is discharged as bottomproduct via an outflow 13. The amount of heat required for thedisproportionation of SiHCl₃ is introduced into the reaction column bymeans of the beat exchanger 5.

Above the reaction zone, an intermediate condenser 6 is provided for thelower-boiling SiH₄-containing product mixture ascending in the reactionzone 2. In this condenser, the SiH₄ concentration in the lower-boilingSiH4-containing product mixture is increased by partial condensation ofhigher-boiling components of the lower-boiling SiH₄-containing productmixture at a temperature between −25° C. and 50° C., preferably between−5° C. and 40° C. The heat of condensation is dissipated by a coolantflowing through the intermediate condenser 6. The lower-boiling productfractions of the lower-boiling SiH₄-containing product mixture which arenot condensed in the intermediate condenser 6 are introduced into arectifying section 7 which is arranged downstream of the intermediatecondenser in the direction of flow of the ascending product fractions,and further concentrated. In the embodiment of FIG. 1, the rectifyingsection 7 is inserted above the intermediate condenser 6 and integratedinto the reaction column 1. Alternatively, the rectifying section can bearranged outside the reaction column. The product mixture from therectifying section 7 is finally taken off at the top of the reactioncolumn via an outlet 8 and introduced into an overhead condenser 9 inwhich it is condensed and discharged in liquid form, as final SiH₄product obtained, via an SiH₄ product line 10. Part of the recoveredSiH₄ is returned to the top of the reaction column 1 via a branch line11. The branch line 11 opens into the column above the rectifyingsection 7.

Residual inert gas fractions obtained in the overhead condenser 9 duringSiH₄ condensation are discharged from the overhead condenser via aninert gas line 12.

According to the invention, in the embodiment of FIG. 1, condensation ofthe product taken off at the top of the reaction column 1 in theoverhead condenser 9 produces silane in a concentration of >70%,preferably >90%, particularly preferably >98%. Followingdisporportionation of SiHCl₃ in the reactive/distillative reaction zone2, the lower-boiling SiH₄-containing product which is ascending from thereaction zone to the top of the reaction column 1 is subjected to anintermediate condensation. Instead of one intermediate condenser, asdescribed in the embodiment above, a plurality of intermediatecondensers can be inserted. The intermediate condenser(s) 6 operate attemperatures at which the removal of the heat of condensation by meansof a coolant is still possible between −25° C. and 50° C., preferablybetween −5° C. and 40° C., so that only a considerably smaller,uncondensed fraction of the SiH₄-containing product mixture has to betransferred to a rectifying section 7 equipped with conventionaldistillation internals such as trays and packings, and only the gasfraction exiting the rectifying section has to be condensed in theoverhead condenser 9 at very low temperatures in a final step.

Moreover, the rectifying section 7 including its associated overheadcondenser 9 can also be arranged externally outside the reaction column1.

With conventional pressures of 1 to 50 bar, preferably 1 to 10 bar, andthe desired purities of the silane product, the overhead condenser 9 hasto be operated below the condensation temperatures of <−40° C., in mostcases even below <−60° C. By installing purely distillative separationsections upstream of the condensation of the final silane product andarranging a distillative stripping section 4 above the bottom evaporator5, the energy introduced is used several times, i.e. (1) for purifyingand concentrating the silane in the rectifying section 7, (2) forcontinuous distillative removal of those intermediates or products whichare lower-boiling under the respective local conditions in the apparatusand thus for increasing the reaction rate in the reactive/distillativereaction zone 2, and (3) for purifying the SiCl₄ in the lower part ofthe reaction column. A further advantage compared to the processdisclosed in DE 2 507 864 results from the distillative strippingsection 4 and the resulting possibility of purifying the SiCl₄ dichargedat the bottom, because a downstream SiCl₄ purification column can beomitted, thus reducing the energy required for this process step.

Another embodiment is shown in FIG. 2. In this embodiment, theconstruction of the reaction column 1 a is similar to the design of thereaction column 1 of FIG. 1. Therefore, all equipment parts designed inanalogy to the parts of FIGS. 1 and 2 are given the same referencesymbols, but are represented with the added index “a” to distinguishthem.

In the embodiment of FIG. 2, the separation column 14 is arrangeddownstream of a condenser 9 a which is located between rectifyingsection 7 a and separation column 14. In the condenser 9 a, all or partof the uncondensed SiH₄-containing product mixture exiting therectifying section 7 a via the outlet 8 a is condensed prior to enteringthe separation column 14, so that a product mixture which is moreconcentrated in SiH₄ is introduced into the separation column 14. Partof the condensate obtained in the condenser 9 a is returned, via abranch line 11 a, to the reaction column la above its rectifying section7 a. The remaining part of the condensate is compressed by means of aliquid pump 15 and transferred to the separation column 14 via apressure line 16. If only part of the product mixture exiting therectifying section 7 a is condensed in the condenser 9 a, the remainingpart is sucked off via an outlet 12 a by means of a compressor 17,compressed and introduced into the separation column 14 via a pressureline 16′. Alternatively, the stream 12 a can be transferred to a workupstep.

An outlet 18 leads from the top of the separation column 14 to anoverhead condenser 19 from which the condensed silane obtained isdischarged in an SiH₄ product line 20, Part of the liquid silane isreturned to the separation column 14 in a branch line 21. Inert gasesobtained in the overhead condenser are discharged via an inert gas line22.

The bottom product of the separation column 14 is discharged from thebottom 23 of the separation column via a bottom outlet 24. Part of thebottom product flows back into the reaction column 1 a via the branchline 25, another part is returned to the bottom zone of the separationcolumn 14 via a return line 26 after evaporation in the heat exchanger27, another part can be bled off (28) completely from the plant in orderto remove impurities.

In the embodiment of FIG. 2, a liquid or gaseous overhead product havinga lower silane purity of between 25% to 90% is produced by reducing thereflux compared to the embodiment of FIG. 1 and complete or partialcondensation in the condenser 9 a so as to increase the condensationtemperature in the overhead condenser 9 a and to reduce further thecondensation energy which has to be removed at a very low temperature.This overhead product is then purified further by separation in thedownstream separation column 14, where the same pressure or preferably ahigher pressure than in the reaction column 1 a, preferably 15 bar to100 bar, is set, so that the separation column 14 operates at highertemperatures than the reaction column 1 a, based on the samecomposition. In this variant too, the bottom product of the separateseparation column 14 may contain large proportions of trichlorosilane,dichlorosilane and monochlorosilane, depending on the operatingconditions selected. All or part of the bottom product is returned tothe reaction column 1 a via the branch line 25 connected to the outlet24. If necessary, impurities can be removed (28) from the system bybleeding off a part-stream.

The feed(s) introduced into the reaction column via the inlets 3, 3 aand 25, if desired after preliminary reaction in a preliminary reactor,are introduced into the stripping section 4, 4 a, or betweenreactive/distillative reaction zones 2, 2 a and stripping section, orinto the reactive-distillative reaction zone, or into the overheadcondenser 6, 6 a, depending on the respective composition.

The process according to the invention is conducted at pressures from 1to 50 bar, preferably 1 to 10 bar, particularly preferably 2.8 to 5 bar,in the reactive/distillative reaction zone using catalytically activesolids. The temperatures in the system are varied by means of thepressures. The temperatures in that part of the reactive/distillativereaction section in which the disporportionation takes place are between30° C. and 180° C., preferably between 50° C. and 110° C. Thetemperature which is to be set in each case depends on the range inwhich the catalytically active solids are stable.

A disadvantage of the previously described processes for thedistillative separation of pure silane with concomitant reaction is thelarge amount of heat which has to be removed at the condensationtemperature of the silane at a given pressure, i.e. for example at −50°C. to −120° C. As mentioned above, condensation at these temperatures iseconomically very unfavorable. As the amount of heat which has to beremoved during operation without intermediate condenser is of the sameorder as the amount of heat introduced at the bottom of the reactioncolumn, the heat removal costs should generally be considerably higherthan the heat introduction costs. This is largely avoided by theintermediate condensation according to the invention. For example,depending on the system pressure, 60% to 97% of the heat of condensationcan be removed when using a coolant having a temperature of 25° C. forthe intermediate condensation to cool down the gas stream exiting abovethe intermediate condenser(s) to 40° C., so that only 3% to 40% of theheat of condensation have to be removed at the condensation temperatureof the silane. Nevertheless, purification of the silane to give an SiH₄content of preferably more than 90%, particularly preferably more than98%, is possible above the intermediate condenser in a separation columnplaced directly above the intermediate condenser and/or in a separateseparation column, the condenser for condensing silane at the head ofthe separation column being operated at a coolant temperature below thecondensation temperature of the silane.

Owing to the intermediate condensation, the conditions in the reactionareas in the reactive/distillative reaction zone remain essentiallyunchanged compared to a reaction column without intermediate condenser,so that intermediates and products formed can still be separatedeffectively by distillation after their formation. It is only above theintermediate condenser that the vapor and liquid streams aresignificantly reduced compared to the rest of the system. However, theyare sufficient to ensure that the silane which is present in smallamounts compared to the bottom product of the reaction column, SiCl₄,and whose boiling point differs considerably from the remainingcomponents, is concentrated in a separation column placed on top or in aseparate separation column, achieving purities of >50%, particularlypreferably >98%.

Preferred internals used in the reaction columns of the installationaccording to the invention are those which ensure an intensive masstransfer between gas phase and liquid phase and simultaneously allow anintensive contact with the solid catalyst. Owing to the combination ofmass transfer and reaction, a sufficient distance from the respectivereaction equilibrium is ensured in the reactive/distillative reactionzone by rapid separation of products formed, so that the reaction alwaysproceeds with a high reaction rate. Examples of such column internalsare trays, structured or random packings for introducing heterogeneouscatalysts, as described, for example, in the following publications: EP670 178, EP 461 855, U.S. Pat. Nos. 5,026,459, U.S. 4,536,373, WO 94/08681, WO 94/08 682, WO 94/08 679, EP 470 655, WO 97/26 971, U.S. Pat. No.5,308,451, EP 755 706, EP 781 829, EP 428 265, EP 448 884, EP 640 385,EP 631 813, WO 90/02 603, WO 97/24 174, EP 665 041, EP 458 472, EP 476938 and German Utility Model 298 07 007.3. Alternatively, the solidcatalyst can be spread on distillation trays as such or in agglomeratedform. When carrying out the process, residence time, catalyst volume anddistillative separation effect in the reaction zone are matched toreaction kinetics and mass transfer kinetics, the parameter optimumdepending strongly on the boundary conditions, such as the catalystselected, the system of substances and the pressure and temperatureconditions selected.

Alternatively, the catalyst can be introduced into external, optionallythermostatted reactors, alternating between transferring the liquidphase from the reaction column into the reactor and from the reactorback to the column for separation of substances.

In this case, however, it is disadvantageous that products formedgenerally cannot be separated by distillation as rapidly after theirformation as in the case of the abovementioned trays, structuredpackings and random packings. Decoupling of different temperatures inthe column and in external reactions can be achieved by thermostattingthe material streams between the column and the reactors.

FIG. 3 shows the distillative/reactive reaction zone 2; 2 a of FIGS. 1and 2 for the embodiment having external reactors. The liquid mixtureflowing out of a distillative section 29 enters, optionally via heatrecovery unit and thermostatting unit 31, a reactor 32 operated indownward or upward flow mode, and is passed on into the subsequentdistillative section. The sequence “distillative section/thermostattingunit/reactor” can be repeated on top of one another any number of times.

According to the invention, the disproportionation which is taking placein the reaction zone of the reaction columns is supplemented by a purelydistillative separation and purification of the silane- or silicontetrachloride-containing products to be discharged at the top and at thebottom of the reaction columns. The distillative separation is carriedout by means of conventional internals for pure distillation such astrays, structured packings and random packings. For the exitinghigher-boiling SiCl₄ component it is convenient to produce asubstantially concentrated silicon tetrachloride bottom productcontaining more than 70% of SiCl₄, preferably more than 95% of SiCl₄,particularly preferably more than 99% of SiCl₄, by purely distillativeseparation below the reactive/distillative reaction zone in the bottompart of the reaction column, and to take off this product at the bottomof the reaction column.

List of Reference Symbols

-   Reaction column 1, 1 a-   Reactive/distillative reaction zone 2, 2 a-   Catalyst bed 2′, 2 a′-   SiHCl₃ inlet 3, 3 a-   Distillative stripping section 4, 4 a-   Bottom evaporator 5, 5 a-   Intermediate condenser 6, 6 a-   Intermediate condenser 7, 7 a-   Vapor outlet 8, 8 a-   Overhead condenser 9, 9 a-   SiH₄ product line 10, 10 a-   Branch line 11, 11 a-   Inert gas line 12, 12 a-   SiCl₄ outflow 13, 13 a-   Separation column 14-   Liquid pump 15-   Pressure line 16-   Compressor 17-   Outlet 18-   Overhead condenser 19-   SiH₄ product line 20-   Branch line 21-   Inert gas line 22-   Bottom 23-   Bottom outlet 24-   Branch line 25-   Return line 26-   Heat exchanger 27-   Bleed-off 28-   Distillation section 29-   Heat recovery unit 30-   Thermostatting unit/heat exchanger 31-   Reactor 32

1. A continuous process for the preparation of silane of formula SiH₄ bycatalytic disproportionation of trichlorosilane of formula SiHCl₃ toform SiH₄ and silicon tetrachloride of formula SiCl₄ in areactive/distillative reaction zone comprising (a) introducing SiHCl₃into a reactive/distillative reaction zone comprising a catalyst bed ofa catalytically active solid at a pressure of 1 to 50 bar to form alower-boiling SiH₄-containing product and a higher-boilingSiCl₄-containing bottom product; (b) removing the lower-boilingSiH₄-containing product from the reactive/distillative reaction zone andcondensing the SiH₄-containing product in an intermediate condensationat a temperature in the range from −5° C. to 40° C.; (c) introducing thelower-boiling SiH₄-containing product which is not condensed in theintermediate condensation into a rectifying section and increasing theSiH₄-concentration in the SiH₁-containing product which is not condensedin the intermediate condensation; (d) further condensing anySiH₄-containing product that is not condensed in the intermediatecondensation and concentrated in the rectifying section in an overheadcondenser from which the SiH₄-containing product is discharged as finalproduct.
 2. A process according to claim 1 wherein the pressure in thecatalyst bed is from 1 to 10 bar.
 3. A process according to claim 1wherein the SiH₄-containing product discharged is separated in theoverhead condenser at a pressure higher than the pressure employed inthe intermediate condensation.
 4. A process according to claim 1 whereinall or part of the chlorosilane is returned to the reactive/distillativereaction zone.
 5. A process for producing silane, the process comprisingthe steps of: providing a reactive/distillative reaction zone includinga catalyst bed of a catalytically active solid forming a lower-boilingSiH₄-containing product and a higher-boiling SiCl₄-containing bottomproduct; introducing SiHCl₃ into the reactive/distillative reaction zoneat a pressure of 1 to 50 bar and forming the lower-boilingSiH₄-containing product and the higher-boiling SiCl₄-containing bottomproduct; removing the lower-boiling SiH₄-containing product from thereactive/distillative reaction zone; cooling the SiH₄-containing productafter said removing in an intermediate condensation with temperatures inthe range from −5° C. to 40° C.; providing a rectifying section;introducing the lower-boiling SiH₄-containing product which is notcondensed during said cooling into a rectifying section to increasing aSiH₄-concentration in the SiH₄-containing product; condensing theSiH₄-containing product from the rectifying section in an overheadcondenser form which the SiH₄-containing product is discharged as finalproduct.
 6. An installation for the continuous preparation of silane offormula SiH₄ by catalytic disproportionation of trichlorosilane offormula SiHCl₃ to form SiH₄ and silicon tetrachloride of formula SiCl₄in a reaction column having (1) a reactive/distillative reaction zonecomprising a catalyst bed made of solid bodies of catalytically activesolid and through which the disproportionation products andtrichlorosilane can flow, (2) an inlet for introducing SiHCl₃ into thereactive zone, (3) an overhead condenser connected to the reactioncolumn for condensing the SiH₄-containing product that is formed andhaving an outlet for condensed SiH₄ at the overhead condenser, (4) atleast one intermediate condenser arranged between thereactive/distillative reaction zone and the overhead condenser, whereinthe at least one intermediate condenser is operated at a temperature inthe range from −5° C. to 40° C., (5) a rectifying section for increasingthe SiH₄-concentration in the lower-boiling SiH₄-containing productwhich is not condensed in the at least one intermediate condenser beingarranged downstream of the at least one intermediate condenser in adirection of flow of the lower-boiling SiH₄-containing product comingfrom the at least one intermediate condenser, and (6) an outflow forSiCl₄ obtained as bottom product, for carrying out the process accordingto claim
 1. 7. An installation according to claim 6 wherein the at leastone intermediate condenser is arranged above the catalyst bed.
 8. Aninstallation according to claim 6 wherein a separation column forseparating SiH₄-containing product fractions from higher-boilingchlorosilane components is arranged downstream of the at least oneintermediate condenser in a direction of flow of the lower-boilingproduct mixture coming from the at least one intermediate condenser. 9.An installation according to claim 8 wherein the separation column isarranged downstream of the rectifying section.
 10. An installationaccording to claim 9 wherein the overhead condenser is arranged betweenthe rectifying section and the separation column.
 11. An installationaccording to claim 8 wherein the separation column is operated at apressure higher than the pressure in the at least one intermediatecondenser and the product that is conducted to the separation column iscompressed.
 12. An installation according to claim 8 wherein a branchline that opens into a reactive/distillative reaction zone of thereaction column is connected to a bottom outlet of the separationcolumn.